1. Field of the Invention
The present invention relates to a method and a device for determining state of a battery, and a battery power supply system, for determining SOF or SOH of a battery.
2. Related Arts
The technology for determining state of function (SOF) (i.e., discharge capability) or state of health (SOH) (i.e., deterioration level) of a battery by monitoring a battery is, especially in the field of vehicles or the like, an extremely important technology in order to achieve safe and comfortable driving. A method for determining SOF or SOH of a battery has been proposed until now. For example, a method disclosed in Japanese Patent Application Publication No. 2005-037380 has been known.
As for the method disclosed in Japanese Patent Application Publication No. 2005-037380, SOF or SOH of a battery is determined on the basis of the internal impedance or internal resistance of a battery. That is, when the response voltage calculated from the internal impedance or internal resistance of the battery becomes less than or equal to a predetermined threshold, it is determined that the SOF of the battery is lacking, or the SOH thereof is low. In this case, as internal impedance or internal resistance varies with temperature and state of charge (SOC) of a battery, it is required that the voltage between terminals being used for the determination be converted to the value at a predetermined temperature and SOC.
Also, in Japanese Patent Application Publication No. 2005-037380, it is reported that a response voltage subjected to a constant current discharge has a linear relation with the internal impedance, on the condition that temperature and SOC of a battery are constant. According to the disclosure, in the case where the temperature and the SOC of the battery satisfies with a prescribed condition, it is possible to determine SOF or SOH of the battery by obtaining the above mentioned response voltage.
However, in the actual battery power supply systems, particularly, in batteries for vehicles or other, the condition of temperature and SOC of the battery been kept at a constant state almost has not been achieved. In practice, the temperature and the SOC vary with the operating conditions or the like, and the correlation between the response voltage and the internal impedance or the internal resistance used as an index for SOF or SOH, varies with the change of the temperature and the SOC. Therefore, in the case of calculating a response voltage by using a correlative function of internal impedance or internal resistance, it is required that the correlative function is corrected responding to the variation of the temperature and the SOC.
As described above, it is required that the internal impedance or the like used for determining SOF or SOH of the battery is corrected for the effect of the temperature and the SOC of the battery. As one of conventional methods for performing temperature correction with high accuracy, for example, a method described in Japanese Patent Application Publication No. 2005-091217 is known. In the Japanese Patent Application Publication No. 2005-091217, a method for forecasting calculation of the internal impedance at any temperature from the internal impedance measured at a certain temperature is disclosed.
Besides, in recent years, the use of a portable terminal unit or the like as an electronics device is expanding, and the importance of a battery mounted on portable terminal units or the like is increasing. Also, in the field of vehicle, along with the prevailing of start-stop system, the technology which can grasp state of battery accurately has come to be desired strongly. Thus, along with the importance of battery rising considerably, the necessity of detecting state of a battery, by monitoring the battery, arises naturally. To cope with this, the art for estimating SOH or SOF of a battery has been proposed so far.
Conventionally, as a method for estimating SOH or SOF of a battery, a method using internal impedance or internal resistance of a battery as an index has been contrived. According to this method, there rises a problem that determining true SOH and SOF is difficult, because the value of internal resistance or internal impedance is affected by the temperature or SOC of the battery. In order to resolve such a problem, for example, the art disclosed in Japanese Patent Application Publication No. 2001-228226 is proposed.
In the Japanese Patent Application Publication No. 2001-228226, a method that making a temperature correction for internal impedance, and then comparing the corrected value with a threshold determined responding to SOC is proposed.
However, as described above, as it is required that a correlative function between the response voltage at constant current discharge and the internal impedance or the internal resistance is corrected responding to the deviation of temperature and SOC of a battery, the art for correcting the coefficients of the correlation function with high accuracy has not been know until now. Therefore, there is a problem that SOF and SOH of a battery can not be determined with high accuracy.
In the art disclosed in the Japanese Patent Application Publication No. 2005-037380, a concrete method for making a temperature correction for internal resistance is not disclosed. And, the method is such a complicated as to need making a correction for determination threshold as well as for internal resistance, thus, there is a problem that handling the method is difficult. Besides, in order to estimate SOF by using this method, there needs for calculation momentarily with tracing application process, thus, the forecasting calculation of internal impedance value responding to the temperature and the SOC at each moment is needed. Accordingly, in practice, there is a problem that the art disclosed in Japanese Patent Application Publication No. 2005-037380 can not fully evaluate as SOF.
Also, in the art disclosed in the Japanese Patent Application Publication No. 2005-091217, there is no description of the effect caused by SOC, and there is a problem that the art can not fully respond to determining SOH and SOF, when the effect caused by SOC is strong. As the effect caused by SOC becomes strong in a region of the low SOC, thus, the art disclosed in the Japanese Patent Application Publication No. 2005-037380 becomes difficult to fully respond to the battery which is supposed to be used under such a condition.
So, the present invention is made to solve these problems. An object of the present invention is, by correcting the effect caused by the change of temperature and the SOC of the battery, to provide a method for determining state of a battery so as to determine SOF and SOH with high accuracy.